FIG. 10 is cross-sectional views of conventional read labels used as an information recording medium. As shown in FIG. 10 (a), the read label used as an information recording medium includes: an adhesive layer 3a disposed on a base material 2a; a pigment layer 17a disposed on the adhesive layer 3a; a laser marking layer 18a disposed on the pigment layer 17a, and a protective film layer 5a disposed on the laser marking layer 18a. 
In FIG. 10(b), a color-developed layer 19a is formed by radiating a laser beam 7a onto the laser marking layer 18a from a laser device such as carbon dioxide laser or YAG laser.
At this point, a desired marking position of the laser marking layer 18a is irradiated with the laser beam 7a from the laser device to generate a color only in the desired portion, thereby forming the color-developed layer 19a. The laser beam 7a to be used depends on the material of the laser marking layer 18a. Information is read by distinguishing or identifying the desired marking from a color difference between the color-developed layer 19a and the pigment layer 17a disposed under the laser marking layer 18a (similar techniques are disclosed by, for example, Patent Literatures 1 and 2 listed below as related art documents).